This invention relates to an exhaust gas cooler for reducing the temperature of exhaust gases from internal combustion engines. In particular the invention relates to an exhaust gas cooler in which a coolant is passed around passages through which the exhaust gas travels.
FIGS. 1a to 1c show a known exhaust gas cooler. This prior art cooler comprises a circular tube 1 which has tapered ends 2 which serve as entry 3 and exit 4 orifices for exhaust gases. The orifices are provided with flange plates 10 for connection to exhaust pipes. The ends of the tube are sealed by circular tube plates 5 which define a coolant chamber inside the tube. Each tube plate 5 has a number of circular holes 6 arranged through it. The holes 6 in each tube plate 5 are connected by a number of small diameter tubes 7 which are sealed at one end to the first tube plate and at the other end to the second tube plate. Exhaust gases flow into the entry orifice 3, along the inside of the small diameter tubes 7 and out of the exit orifice 4. The exterior of the tube is provided with entry and exit nozzles 8, 9 which communicate with the coolant chamber for the supply of coolant liquid. A bracket 11 is fixed to the tube for mounting the exhaust gas cooler.
Similar prior art exhaust gas coolers are known for example from U.S. Pat. No. 4,685,292. In all the prior art coolers the tubes which carry the exhaust gases are arranged within a cooling chamber of circular cross-section. This results in exhaust gas coolers which are bulky and inefficient in their use of space and do not fit easily within the frequently cramped engine layout. It is an object of the present invention to provide an exhaust gas cooler which is more compact in shape and yet provides flow characteristics comparable or superior to prior art gas coolers.
According to a first aspect of the present invention there is provided an exhaust gas cooler comprising:
an external tube having first and second end walls within said tube, said external tube and end walls defining a coolant chamber between said end walls and first and second exhaust gas chambers outside said first and second end walls respectively,
coolant inlet and outlet means communicating with said coolant chamber,
a plurality of internal tubes extending from said first end wall to said second end wall and arranged such that the interior of each internal tube communicates with said first and second exhaust gas chambers, and
exhaust gas inlet and outlet means communicating with said first and second exhaust gas chambers respectively,
wherein the external tube has a cross-sectional shape which has a height in the major axis which is greater than its width in the minor axis perpendicular to the major axis.
Preferably the cross-sectional shape of the external tube is substantially oval, most preferably it comprises two semi-circles connected by common straight line tangents parallel to the major axis. Such a cross-sectional shape means that the exterior tube has a planar face which simplifies the fitting of mounting brackets and placement within an engine compartment. An oval shape offers advantages over rectangular cross-sectional shapes, since the tube is less prone to cracking, and sharp re-entrant angles in the tube are avoided, reducing stress concentration.
Preferably the internal tubes are circular in cross-section. It has been found that circular tubes are less prone to clogging with particles carried by the exhaust gases than rectangular tubes, because they do not present internal corners in which particulate matter can collect.
Preferably the internal tubes are arranged in a hexagonal close packed arrangement, such that each internal tube is spaced by the same spacing from its closest neighbouring internal tubes. Preferably the spacing is less than 2 mm, most preferably less than 1 mm. Preferably the spacing is between 10% and 20% of the diameter of the tubes.
Preferably the exhaust gas cooler is made from stainless steel.
Preferably each of the exhaust gas inlet and outlet means comprises a flange plate adapted to connect to a corresponding flange plate on a connecting exhaust pipe and having an aperture therein to permit the through flow of exhaust gases. Preferably each of said first and second exhaust gas chambers is further defined by a tapering cylindrical member extending from said aperture to said external tube.
Preferably the coolant inlet and outlet means comprise tubular pipes adapted to be connected to a coolant hose, most preferably extending substantially in the plane containing the longitudinal axis of the external tube and the major axis of the cross-section of the external tube. Preferably the coolant inlet means is located adjacent to one of the first and second end walls and the coolant outlet means is located adjacent to the other of the first and second end walls. Preferably the coolant inlet and outlet means extend from opposite sides of the external tube.
Preferably a longitudinally extending portion of the coolant chamber adjacent to each of the coolant inlet and outlet means has no internal tubes extending therethrough, such that it forms a coolant passage having an unobstructed area. This may be achieved by omitting a row of internal tubes from the close-packed arrangement at the top and bottom of the external tube. Preferably the unobstructed area has a minimum transverse dimension greater than the diameter of an internal tube. Preferably the unobstructed area of each passage extends over at least 10% of the internal height of the external tube, most preferably at least 15%.